Finishes for hempcrete - The Hempcrete Topic: Designing and Building with Hemp-lime - page 426

posed to any other are discussed in greater detail in Chapter 22 , but the main principles are
as follows:
A vented air gap should be included between the cladding and the face of the hemp-
crete.
Wherever possible, cladding should be of natural, breathable materials.
Steps must be taken to ensure airtightness on the face of the hempcrete, if it is not
rendered underneath the cladding.
Since part of the frame needs to be near the surface of the hempcrete wall to make fix-
ing the cladding possible, it therefore has increased vulnerability to moisture ingress,
and steps should be taken at the design stage to mitigate this.
A system that has been used successfully on strawbale buildings but not so far, to our
knowledge, on a hempcrete wall, is a combination of timber cladding and render. A pro-
tective lime render is applied to the wall and a timber rain screen cladding is fixed over
this. A rain screen is a less robust form of cladding, which is constructed by butting up tim-
bers against each other. It is not as protective as a shiplap or tongue-and-groove cladding,
but since the hempcrete wall below is rendered, the rain screen is not the only protection
for the hempcrete, and a more basic and cheap timber - even recycled timber - can be
used, as long as it is durable enough to withstand external conditions.
Similarly, because the rain screen is acting as the main barrier, the render does not need to
be as strong, durable or decorative as it would be if it were acting alone. This might mean,
for example, that a single very roughly applied basecoat of lime render could be used,
or even an earth render - perhaps made from clay-rich subsoil excavated during ground
works.
In other words, the combination of materials means that both the render and the cladding
can be 'lower spec' than they would be normally, and this therefore offers a cost-effective
solution that may appeal to self-builders, who may not necessarily have the skill to create
a beautiful render finish or the money to pay for purpose-cut, profiled cladding.
Floor finishes
Finishes applied to a breathable hempcrete floor slab must be not only vapour permeable
but also hard-wearing. Whatever finish is used, it is extremely important that the floor is